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how to wire 12 blue leds? with 9 volt ?not enuf info on packaging? Answered


I, and others,  keep posting this LED calculator site - It has all the information you need All you need to do is read and apply.

so it gives me the resistor but how do i wire 12 leds in series just one resistor? resistor to each?

That's a great example where the wizard is out and out wrong. There is no headroom to control the current, and the brightness will be a strong function of battery volts and device temperature.

Using ICENG's figures it produces this - exactly what he said!

Needs correct figures I was just illustrating the process.


Yes, but what it shows is a lack of intelligence in the "wizard" which should surely at least post an advisory on the lack of headroom.


NOTE in the reply below I have inserted values for the LEDS YOUR values may be different so use your correct values.


6 years ago

Blue LED = 3.6 V @ 20 ma
Put two LEDs in series with a 90 ohm resistor to 9 VDC
Do this six times.
There and here you are......A

soo 9 v battery 90 ohm resistor and just series every two?

Only in Hollister :-)

Two blue use 7.2 V
Resistor gets to see the left over voltage 9 - 7.2 = 1.8 V
Resistance = V / I = 1.8 V / o.02 A = 90 ohms
Power of resistor = V * I = 1.8 V x o.02 A = o.036 W less them ¼ Watt
Even less then 1/8 Watt..............   A

so resistor is on negitive of the series

You pick Negative, in-between or positive side,
Builders choice.

-il -----|<|------|<|-----/\/\/\/\-----+9V

If you don't find a 90 try a 100 ohm


please tell me the easyest way to wire 12 blue leds to a 9 volt battery i dont need the math just the help on the way to do it

Not enough info in the question.